According to the “pigeonhole principle”, if we randomly select 367 people, there must exist two people having the same birthday. However, it is surprising to know that if we select only 23 people randomly, the probability where two of them have the same birthday is higher than 0.5. Moreover, for a random selection of 27 people, the probability is higher than 0.6. Whereas for a random selection of 41 people, the probability is higher than 0.9. And for a random selection of 60 people, the probability is higher than 0.99!